Natural and artificial monocrystalline diamonds have been used for various applications because of their excellent properties. A tool including monocrystalline diamond is, for example, a water jet orifice (Patent Document 1), a stylus for gravure printing (Patent Documents 2 and 3), a scriber (Patent Document 4), a diamond cutting tool (Patent Documents 5 and 6), or a scribing wheel (Patent Document 7).
However, such monocrystalline diamond also has a property that abrasion losses vary (uneven wear) depending on crystal orientations of the diamond. For example, abrasion loss considerably varies between the (111) plane and the (100) plane. For this reason, monocrystalline diamond applied to such tools described above is worn away only in a specific plane in a short time as the tools are used, and predetermined effects are not provided, which has been a problem.
Monocrystalline diamond also has a property of cleaving along the (111) plane. For this reason, when monocrystalline diamond is applied to a tool subjected to a stress during use, the tool breaks or cracks, which also has been a problem.
To deal with the property of uneven wear and the cleaving property of monocrystalline diamond, sintered diamond may be used. Such sintered diamond is obtained by sintering diamond grains with a metal binder such as cobalt and hence the metal binder is present among the diamond grains. The metal binder region is softer than the diamond grains and hence is worn away in a short time. As the amount of the binder decreases, the diamond grains come off and the effects are not provided with stability for a long period of time. There is also a problem in that adhesive wear occurs between the metal binder region and a metal material being worked and working for a long period of time cannot be performed.
To solve such a problem caused by a metal binder, a binderless sintered diamond may be produced by dissolving the metal binder with acid to thereby remove the metal binder. However, removal of a metal binder reduces the binding power of diamond grains, which most likely increases abrasion loss.
For polycrystalline diamond free from a metal binder, there is a polycrystalline diamond obtained by chemical-vapor deposition (CVD). However, this polycrystalline diamond has a small binding strength among grains and hence suffers from large abrasion loss, which has been a problem.
Hereinafter, the above-described tools are specifically described.
A water jet orifice including monocrystalline diamond has a problem in that a target cutting width is no longer achieved after the lapse of usage time.
This is caused by the following mechanism. In such an orifice composed of monocrystalline diamond, diamond crystals in the interior surface of an orifice bore have various crystal orientations toward surroundings. The orifice having the shape of a cylinder at the initial stage of use suffers from abrasion in a plane susceptible to abrasion in a short time. As a result, the cylindrical shape of the orifice is lost and the interior surface is expanded into the shape of a polygon such as hexagon.
To deal with such deformation into a polygonal shape caused by uneven wear, sintered diamond may be used (Patent Document 8). However, this causes coming off of diamond grains with a decrease in the amount of a binder as described above and an orifice bore is expanded. Thus, a cutting width is not provided with stability for a long period of time, which is a problem. In particular, a water jet intended to provide enhanced cutting efficiency is configured to expel liquid containing water and rigid particles (alumina or the like) at a high pressure. As a result, a metal binder region, which is softer than diamond grains, wears away in a short time and a cutting width is not provided with stability for a long period of time, which is a problem.
To cover the interior surface of an orifice with polycrystalline diamond free from a metal binder, a method may be used in which the interior surface of a metal orifice bore is coated with a diamond thin film free from a metal binder by CVD (chemical-vapor deposition) as described above (see Patent Document 9). However, such a diamond thin film has a short wear life, and has a small binding strength among grains and hence has a short wear life, which has been a problem.
Another example is a stylus for gravure printing in which natural or artificial monocrystalline diamond is used as material for the stylus (see Patent Documents 2 and 3). However, possibly because such diamond has a property of cleaving, such a tool breaks or cracks by a stress during use, which is a problem. Due to the property of uneven wear, such diamond is worn away only in a specific plane in a short time as the tool is used, and hence working for a long period of time cannot be performed, which has also been a problem.
Still another example is a scriber including monocrystalline diamond. For example, as shown in Patent Document 4, polyhedron-shaped monocrystalline diamond is used to scribe monocrystalline substrates, glass substrates, and the like with a vertex of the polyhedron, the vertex serving as a blade. Such a scriber composed of monocrystalline diamond is produced by working monocrystalline diamond such that the (111) plane, which is the most resistant to abrasion against a workpiece that is to be scribed and is composed of a monocrystalline material such as sapphire, is particularly positioned to be aligned parallel to the work to be scribed.
However, possibly because monocrystalline diamond has a property of cleaving along the (111) plane as described above, scribers composed of monocrystalline diamond crack or wear unevenly when a plane used for scribing only slightly deviates from the (111) plane, which has been a problem.
Still another example is a diamond cutting tool in which natural or artificial monocrystalline diamond is used as material for the tool (see Patent Documents 5 and 6). However, because of the problems of the cleaving property and the property of uneven wear of monocrystalline diamond as described above, such a tool composed of monocrystalline diamond has a problem in that the tool breaks or cracks due to a stress during use, is worn away only in a specific plane in a short time as the tool is used, and working for a long period of time cannot be performed.
Still another example is a scribing wheel in which monocrystalline diamond is used as material for the scribing wheel. For example, as shown in Patent Document 7, scribed lines are formed in a brittle material such as glass for liquid crystal panels with the V-shaped edge of the wheel, the edge serving as a cutting edge.
However, as with other tools, such a scribing wheel breaks or cracks due to a stress during use because of the problem of the cleaving property of monocrystalline diamond, which has been a problem.
Due to the property of uneven wear, such a tool is worn away only in a specific plane in a short time as the tool is used, and use of the tool for a long period of time is not possible, which has been a problem. A scribing wheel composed of monocrystalline diamond has a V-shaped edge in which crystals have various crystal orientations in the circumferential direction. Thus, the edge having the shape of a perfect circle at the initial stage of use is worn away in a plane susceptible to wear in a short time and the perfect circular shape is deformed into the shape of a polygon. As a result, the wheel becomes no longer able to roll, which has been a problem.
To deal with the cleaving property and the property of uneven wear in the above-described various tools, a sintered diamond compact may be used as material for such tools, the compact containing metal serving as a binder (Patent Documents 7 and 10).
However, even though sintered diamond is used, the following problems are likely to occur: a metal binder region containing cobalt or the like is softer than diamond grains and hence wears away in a short time, and adhesive wear occurs between the metal binder region and a metal material being worked such as copper and working for a long period of time cannot be performed. Such a metal binder in the sintered diamond compact may be removed by dissolving the metal binder with acid. However, this reduces the binding power of diamond grains, which most likely increases abrasion loss.
Polycrystalline diamond that is produced by CVD and is free from a metal binder has a small binding strength among grains and hence probably has a problem in that such diamond has a short wear life.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2000-061897
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2006-123137
[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2006-518699
[Patent Document 4] Japanese Unexamined Patent Application Publication No. 2005-289703
[Patent Document 5] Japanese Unexamined Patent Application Publication No. 2004-181591
[Patent Document 6] Japanese Unexamined Patent Application Publication No. 2003-025118
[Patent Document 7] Japanese Unexamined Patent Application Publication No. 2007-031200
[Patent Document 8] Japanese Unexamined Patent Application Publication No. 10-270407
[Patent Document 9] Japanese Unexamined Patent Application Publication No. 2006-159348
[Patent Document 10] International Publication No. 2003/051784